(a) Field of the Invention
The present invention relates to a method of preparing water free isothiazolone, more particularly, to a method of preparing water free isothiazolone having a relatively high stability and a method of preparing substantially pure water free 5-chloro-2-methyl-3-isothiazolone having a relatively high antibacterial activity.
(b) Description of the Related Art
Isothiazolones of formula 1 are well known as microbicides and are employed in many industrial and household systems. ##STR1## wherein R1 is selected from the group consisting of hydrogen; unsubstituted or halogen- or hydroxy-substituted (C.sub.1 -C.sub.10) alkyl; unsubstituted or halogen-substituted (C.sub.2 -C.sub.10) alkenyl; unsubstituted or halogen-substituted (C.sub.2 -C.sub.10) alkynyl; halogen atom; unsubstituted or (C.sub.1 -C.sub.10) alkyl- or (C.sub.2 -C.sub.9) alkoxy-substituted aralkyl, and
R2 and R3 are the same or different and selected from the group consisting of hydrogen, halogen and (C.sub.1 -C.sub.4) alkyl respectively. ##STR2##
Among then, 5-chloro-2-methyl-3-isothiazolone of formula 2 has a relatively high antibacterial activity compared to 2-methyl-3-isothiazolone. Therefore, a method of preparing pure 5-chloro-2-methyl-3-isothiazolone is required.
Isothiazolone have a very low stability in a practical condition required a long time storage. A lot of method to improve a stability of isothiazolone have been developed.
U.S. Pat. No. 3,870,595 and U.S. Pat. No. 4,067,878 disclose an isothiazolone stabilization method adding a metal nitrite salt or metal nitrite salt to prevent a chemical decomposition. In certain applications, e.g., preservation of latex emulsion, these metal stabilization salts cause problems which can reduce the performance or value of such systems. Another problem with such metal stabilization salts is that they cause corrosion in certain systems. For example, chloride salts have a corrosive effect on many metals.
U.S. Pat. No. 5,068,344 discloses a process for the preparation of salt free, water free 3-isothiazolone compounds by using an ammonia. This method requires a separating step. In the separating step, 10-20 wt % of total isothiazolone is not separated from the filtered ammonium chloride salt. These cause a lot of wastes. Also, the ammonium chloride, that is not separated from isothiazolone, is accompanied with a final product and give a bad effect on a its stability.
U.S. Pat. No. 5,466,818 discloses a method of producing substantially separated 5-chloro-2-methyl-3-isothiazolone and 2-methyl-3-isothiazolone from a mixture of their hydrochloride salts. This method has a harmful working condition because of hydrogen chloride gas formation. Also, a stability of isothiazolone may decrease because of heating step. This method requires a filtering step to isolate isothiazolone from isothiazolone hydrochloride salt.